Is is generally acknowledged that disc brakes are more effective than drum brakes. Some cars have disc brakes front and rear, and some (usually smaller) cars still have drum brakes on the rear. I’m wondering, why do they still use drum brakes? Some of the answers I came up with are:
They’re cheaper. But then they’d have to be really cheap to justify the cost of a drum brake factory in addition to the disc brake factory.
It prevents rear wheel lock-up. But then even tiny new cars these days have ABS so this shouldn’t be an issue.
So what’s the story? What is the real engineering and economic reason for using drum brakes?
I think part of the reason is it provides balance between the front and rear. the rear needing less stopping force gets the less effective braking system
Drum brakes are cheaper to make than disk brakes; the only advantage of using drum brakes is lower cost.
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And you’ve got it backwards: the drum brake factories came first, then the disk brake factories came along. Disc brakes work better, but it was a simple case of them not wanting to shut down the drum brake factories, because car companies still want to use drum brakes. Lots of new cars in the US still use rear drum brakes.
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If the hand brake still connects to the rear wheels (which it does in most cars), it does function better with a better “locking” on drum brakes (depending where the pivot point of the shoe is, of course…some manufacturers put the pivot point backwards).
It is, as was mentioned, easier to balance braking force for everyday control with drums on the rear and discs on the front.
scr4, this is just a guess, but drum brakes require only one casting for the brake drum; everything else can be stamped out of sheet metal. Disc brakes need two or three castings, one for the disc and one or two for the caliper. The hanger also needs to be made out of metal plate.
This is not true. Why would disk brake systems require power assist? These systems are hydraulic systems, identical in all respects to drum brake systems.
Both discs and drums are hydraulic systems, usually power assisted. Drum brakes are very easy to operate using a cable pull that forces the shoes apart, making it very inexpensive to have an emergency and parking brake.
This is not accurate. Power/no power has nothing to do with the type of brakes. And as a stand-out example, the FIAT X 1/9 was well known for it’s nice and effective brakes, and it had absolutely no power assist on it.
With drum brakes the pivoting of the brake shoe will assist in brake force. This enables drumbrake systems to operate fairly well without a brake booster.
Although it is true that you can have 4 wheel disc brakes with no booster, the pedal effort will be very high compared to drums. On a small, light, car you can still get away with manual discs. Hevy cars will require a booster.
The only advantage to drum brakes (except the lower cost) is that they are not sensitive to water. Disc brakes have a tendency to not work well when driving through deep puddles.
The big problem with drum brakes is that the heat is retained inside the drum, making them overheat during hard use.
Thanks for all the answers so far. About parking/hand brakes, my current car has rear disks and the hand brake operates the caliper, there isn’t an extra drum. I learned all about the working of the hand brake after water got into the cable housing and froze the hand brake on on a really cold winter morning.
even though this one was answered I just had to add that I had a car ('80 dodge omni 024) that had no power brakes (no p/s either) it was a front disk/rear drum and it worked easily enough. I was very surprized when I got a 85 plym turismo a few years later and found that they had power brakes - on such a light car there is really no need and IMHO more dangerous since loss of power assist makes braking much harder.
just wanted to point out that manual brakes do work very good on low end cars.
Whaaat? A vehicle with 4 wheel disc has drum brakes in the back for a parking brake? Where did you get that idea from? Do you have an example of this?
I’ve heard of vehilcles having a drum brake on the driveshaft for a parking brake, but even then, none of those vehicles had disc on the rear wheels either.
A small “sub-drum” used only as the parking brake is one method of doing it on 4-wheel-disc cars, but not the only one.
I’ve no personal experience, but my Haynes Automotive Brake Manual nicely describes three ways to deal with it (going from memory here):[ul][li]cable actuation of the main caliper on the rear wheels[]small caliper (in addition to the main one) used only as the parking brake[]a “top-hat” geometry to the drum: the hat “brim” is the disc, while the insides of the “stovepipe” house a very small drum brake that serves as a parking brake[/ul]They don’t mention specifically how common each of these methods are, but imply that you can find examples of all three without much effort.[/li]
This same manual also suggests that power assist proved necessary from a practical perspective to make disc brakes on road cars feasible. Sure, disc brakes work just fine without it, but like zwede said pedal forces required would be excessive by the standards we’ve gotten used to - at least with disc brakes of reasonable size.
